Pharmaceutical compositions and methods of treatment to prevent and treat corneal scar formation produced by laser irradiation

ABSTRACT

Methods for preventing and treating corneal haze resulting from exposure of the eye to laser irradiation are disclosed. The methods include administration of compositions of wound healing modulators to the eye. Compositions for use in preventing and treating the corneal haze are also disclosed.

This application is a continuation-in-part of U.S. Ser. No. 253,009filed Oct. 3, 1988, now U.S. Pat. No. 4,939,135.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods of treatment and pharmaceuticalcompositions used for the prevention and treatment of corneal haze. Theformation of corneal haze as an artifact resulting from exposure of thecornea to laser irradiation is a new phenomenon. The methods of thepresent invention for the prevention and treatment of corneal hazeinvolve the application of compositions to the eye prior to, during andafter irradiation.

2. Description of Related Art

Ophthalmic operations such as corneal transplants and keratotomiestraditionally are performed by surgeons using cutting instruments. Atthe incision site the cutting edge of these instruments unavoidablydamages several layers of cells on either side of the point of entry.This impairs the ability of the surgical wound to heal without resultingscar tissue. The use of lasers in ophthalmic surgery has developedpartly in an effort to minimize damage to cells as a result ofdisturbance due to instrument incisions. Infrared lasers such as carbondioxide (CO₂) lasers have been used to achieve controlled local ablationor incision of the cornea. In the past, use of CO₂ lasers and mostlasers emitting in the visible spectrum, were known to damage or charcells adjacent to the site of ablation or incision because results arethermally achieved through photocoagulation and/or photovaporization.However, through the improvement of these lasers and techniques, it isnow possible to better control the ablation or incision of the cornea,thereby eliminating or reducing the damaging results.

With respect to lasers emitting in the ultraviolet (UV) range, theradiation decomposes the molecules of tissues photochemically bydirectly breaking intramolecular bonds. Thus, there is not thecharacteristic damage to adjacent cells resulting in photothermalablation.

The use of UV lasers, which emit radiation below about 400 nanometers(nm), and the use of improved CO₂ lasers and most lasers emitting in thevisible spectrum, has dramatically improved the possibilities forophthalmic surgery. For example, corneal transplants and keratotomiesmay be more precisely performed with less damage resulting from theprocedure itself. Methods for conducting ophthalmic surgery using anultraviolet emitting laser are described in U.S. Pat. Nos. 4,665,913 and4,732,148 issued to L'Esperance, both of which are incorporated hereinby reference to the extent that they disclose methods and devices forachieving a predetermined refractive correction by volumetric removal ofcorneal tissue. Removal is through the phenomenon of photoablation ofthe cornea namely, of the epithelium, Bowman's membrane and stromalevels of the cornea, using incident UV laser irradiation. Non UV laserscan now also be used to photoablate the cornea for achieving apredetermined refractive correction through the volumetric removal ofcorneal tissue.

The ophthalmic surgical methods disclosed by, for example, L'Esperanceinclude various procedures for correcting eye disorders attributable toabnormal curvature of the cornea, collectively referred to as laserrefractive keratoplasties (LRK). It has been forecast that the eventualadoption of LRK to ablate the cornea for correction of common myopic orhyperopic conditions will largely eliminate the need for eyeglasses,contact lenses or other methods of vision correction using lenses. LRKcan also be used to correct astigmatisms; remove corneal scar tissue;and excise corneal tissue for accommodation of corneas in cornealtransplants. In addition, LRK and other procedures involving lasers canbe used to perform incisions, including incisions for refractive effectssuch as radial keratotomy.

Even with the improved surgical methods using UV and non UV emittinglasers, such as CO₂ and most lasers emitting in the visible spectrum, acondition known as "corneal haze" may result as a response to use of thelaser during ophthalmic surgery. Corneal haze, as discussed herein, isan artifact which has not been observed as a result of ophthalmicsurgery until the advent of use of these lasers. The artifact is seen asopacification of the cornea, which in humans is composed of anepithelial layer, Bowman's membrane, the stroma, Descemet's membrane andthe endothelium. The artifact resulting from laser surgery is seen indifferent parts of the cornea but particularly in the stroma. When theartifact does appear it can usually only be observed by use of a slitlamp. It is not known precisely why the artifact sometimes occurs afterphotoablation of the cornea. The development of corneal haze is ofpotentially greater concern in those procedures affecting a largesurface of the cornea versus procedures involving laser incisions.

A study was done on the response of the corneal epithelium to excimerlasers (lasers based on the excited state of a halogen atom combiningwith the ground state of a rare gas such as krypton or xenon) due toconcern over use of the lasers in work environments, for example, inisotope separation, thermonuclear fusion, photochemistry and underwatercommunications; see Taboada, et al., Health Physics, Volume 40, pp.677-683 (May, 1981). In that study rabbits were exposed to pulsed laserradiation of 248 nm. The rabbits' corneal epitheliums exhibitedincreasing levels of damage with increasing exposure. As a result ofthis damage, the authors suggested that guidelines for workers exposedto short pulse radiation be redefined.

The corneal haze or artifact to be prevented or treated according to thepresent invention is not a result of the use of lasers in the work area.It is rather a result of purposeful and direct exposure of the cornea tolaser irradiation during ophthalmic surgery. Recent studies have beendone regarding the corneal haze which results from exposure to lasers.For example, in one study, seven patients received laser cornealablation with a 193 nm Questek excimer laser. Post ablation examinationwith a slit beam showed a speckled haze at the interface between theepithelium and stroma; see Del Pero, et al., Human Excimer LaserLamellar Refractive Keratectomy--A Clinical Study, ARVO Annual MeetingAbstract Issue, p. 281, No. 8 (1988). In another study ablation with a193 nm excimer laser resulted in a slight haze in the corneas of rabbitsand primates. The haze was observable by slit lamp but disappeared aftertwo weeks. However, in the rabbits a material resembling plasma membranewas reported in Descemet's membrane, which is located between theposterior surface of the stroma and the anterior surface of the cornealendothelium; see Gaster et al., Excimer Laser Ablation and Wound Healingof Superficial Cornea in Rabbits and Primates, ARVO Annual MeetingAbstract Issue, p. 309, No. 4 (1988). In another study discs were formedin the corneal stromas of rabbits by excimer laser photoablation at 193nm. A stromal haze developed by one month, but corneal transparency didimprove after 6 months; see Tuft et al., Corneal Remodeling FollowingAnterior Keratectomy, ARVO Annual Meeting Abstract Issue, p. 310, No. 7(1988).

With the improvement of lasers, particularly UV, CO₂, and, most lasersemitting in the visible spectrum, and their use in ophthalmic surgery,there has developed a need for prevention of the corneal haze whichresults during ophthalmic procedures involving the use of lasers.

It is an objective of this invention to provide methods of treatment toprevent the appearance of and/or treat corneal haze induced by laserirradiation. It is another objective of this invention to providecompositions for treating eyes before, during or after exposure to alaser which will prevent and/or treat corneal haze.

SUMMARY OF THE INVENTION

Corneal haze is an artifact which may result from the photoablation ofthe cornea during ophthalmic surgery conducted, for example, accordingto the methods described by L'Esperance in U.S. Pat. Nos. 4,665,913 and4,732,148. As defined herein, corneal haze presents a new problem as ithas not been observed as a result of ophthalmic surgery until the use oflasers to sculpt the cornea to achieve a predetermined configuration asa result of photoablation.

According to the present invention, compositions containing agents whichmodulate wound healing are used for the prevention and treatment ofcorneal haze. Agents which can be used in the compositions, alone or incombination with other such agents, include: steroids, growth factors,basement membrane components, anti-oxidants, regulators of collagenstructure, aldose reductase inhibitors, nonsteroidal antiinflammatories,immunomodulators, antiallergics, fatty acid derivatives which areproducts of the arachidonic acid cascade and antimicrobials.

The compositions containing the wound healing modulators are formulatedas solutions, suspensions, emulsions or gels depending on thecharacteristics of the wound healing modulator. The compositions canalso be delivered via use of a collagen shield, contact lenses or othersolid matrixes capable of delivering drugs to the cornea placed on theocular surface.

The compositions are used to prevent or treat corneal haze and areapplied to the eye prior to and/or during surgical exposure to laserradiation and/or postoperatively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to methods of treatment of cornealhaze resulting from laser irradiation of the eye. The invention alsoencompasses compositions which contain agents that modulate woundhealing, said agents referred to herein as "wound healing modulators."For purposes of the present specification the term "wound healingmodulator" is used to identify compounds or compositions that facilitatethe prevention or reduction of corneal haze as that term is used herein,regardless of any theoretical explanation for its development. Forpurposes herein the term "corneal haze" refers to the clouding of thecornea which results from exposure of the cornea to laser radiationduring eye surgery. The compositions containing the wound healingmodulators are useful for prevention and treatment of corneal haze whichresults from surgical exposure to laser radiation. In particular thecompositions are useful for the prevention and treatment of corneal hazeresulting from LRK.

Wound healing modulators, included alone or in combinations in thecompositions of the present invention, include: steroids, growthfactors, basement membrane components, anti-oxidants, regulators ofcollagen structure, aldose reductase inhibitors (ARIs) nonsteroidalantiinflammatories (NSAIs), immunomodulators, antiallergics, fatty acidderivatives, which are products of the arachidonic acid cascade andantimicrobials. All of the wound healing modulators disclosed herein areknown. However, none are known or disclosed, alone or in combinations,for the prevention of corneal haze resulting from exposure to laserradiation during ophthalmic surgery.

Without intending to be bound by any theory as to why corneal haze mayappear, it is believed that one or more of the following events may beoccurring. First, it is believed the corneal haze is a scar resultingfrom actual wound repair taking place after photoblation of the cornea.Second, it is thought that the fibroblasts of the stroma may beimproperly activated in response to the laser. Third, the radiationemitted by the laser may damage collagen fibrils resulting in theirimproper alignment. Fourth, the laser may kill or damage fibroblasts inthe stroma. Fifth, the corneal haze may result from corneal edema whichoccurs following photoablation.

With respect to the first theory, the scar, however subtle, may resultfrom wound repair taking place after photoablation. It may arise due to,for example, improper collagen repair, improper epithelial cell coverageof the cornea, or inflammation.

To prevent or reduce scar formation due to improper collagen repair thefollowing wound healing modulators can be used: steroids, growthfactors, basement membrane components and regulators of collagenstructure.

Steroids are known for their role in controlling inflammation andinhibiting wound healing; see, Olsen et al., The Effect of Steroids onthe Healing of the Corneal Endothelium, Acta Ophthalmologica, 62, pp.893-899 (1984); Singh, Corticosteroids in Corneal Endothelial WoundHealing, Annals of Ophthalmology, Vol. 17, no. 4, pp. 238-243 (April,1985); Woost et al., Effect of Growth Factors with Dexamethasone onHealing of Rabbit Corneal Stromal Incisions, Exp. Eye Res., 40, pp.47-60 (1985); Kossendrup et al., Influence of Cyclosporin A,Dexamethasone, and Benzalkonium Chloride (BAC) on Corneal EpithelialWound Healing in the Rabbit and Guinea Pig Eye, Cornea, 4, pp. 177-181(1985/1986), the contents of all of which are incorporated herein byreference. The positive effect of the delay in wound healing isalleviation or prevention of scar formation possibly due to regulationof the pattern of healing; see for example, Sanchez, et al., Effect ofTopical Steroids on the Healing of the Corneal Endothelium, Inves.Ophth., Vol. 13, pp. 17-22 (Dec. 1974), the contents of which areincorporated herein by reference.

The steroids which can be used according to the present inventioninclude all steroids which are capable of preventing or treating cornealhaze resulting from laser irradiation. This includes corticosteroids,preferably glucocorticoids, and all derivatives and isomers thereof. Forexample, steroids which can be employed in the present invention toprevent and treat corneal haze include: dexamethasone; fluorometholone;medrysone; betamethasone; triamcinolone; prednisone; prednisolone, suchas prednisolone acetate; hydrocortisone and pharmaceutically acceptablesalts thereof; prednicarbate; deflazacort; halomethasone; tixolcortol;prednylidene (21 diethylaminoacetate); prednival; paramethasone;methylprednisolone; meprednisone; mazipredone; isoflupredone;halopredone acetate; halcinonide; formocortal; flurandrenolide;fluprednisolone; fluprednidine acetate; fluperolone acetate;fluocortolone; fluocortin butyl; fluocinonide; fluocinolone acetonide;flunisolide; flumethasone; fludrocortisone; fluclorinide; enoxolone;difluprednate; diflucortolone; diflorasone diacetate; desoximetasone(desoxymethasone); desonide; descinolone; cortivazol; corticosterone;cortisone; cloprednol; clocortolone; clobetasone; clobetasol;chloroprednisone; cafestol; budesonide; beclomethasone; amcinonide;allopregnane acetonide; alclometasone; 21-acetoxypregnenolone;tralonide; diflorasone acetate; deacylcortivazol; budesonide anddeacylcortivazol oxetanone. The above-cited steroids are knowncompounds. Further information regarding the compounds can be found inThe Merck Index Tenth Edition, 1983, and the publications cited therein,the entire contents of which are incorporated herein by reference.Additional examples of steroids which can be used according to thepresent invention include: dexamethasone ether derivatives, which arethe subject matter of the commonly assigned patent application Ser. No.922,810, the entire contents of which are incorporated herein byreference; alkyloid steroids of the pregnane series (Rimexolone)disclosed generally in U.S. Pat. No. 3,947,478 issued Mar. 30, 1976, andspecifically for ophthalmic use in U.S. Pat. No. 4,686,214 issued Aug.11, 1987, the entire contents of both of which are incorporated hereinby reference.

Such steroids and combinations comprising one or more steroids willtypically be combined in the compositions of the present invention atconcentrations of between about 0.1 and 4.0 percent by weight (wt. %).The following steroids are preferred: dexamethasone, prednisolone andfluorometholone. The preferred steroids can be used at concentrationsbetween about 0.125 and 1.0 wt. %.

Growth factors are agents which cause cells to migrate, differentiate,transform or mature and divide. They are polypeptides which can usuallybe isolated from many different normal and malignant mammalian celltypes. Some growth factors can be produced by genetically engineeredmicroorganisms, such as bacteria (E. coli) and yeasts; see, for example,Chapters 10 and 11 of The Molecular and Cellular Biology of Wound Repair(1986), the entire contents of the book of which are incorporated in thepresent specification by reference. Growth factors are known for theirinvolvement in a variety of phenomena as set forth above. For example,epidermal growth factor (EGF) is known to stimulate the proliferation ofepidermal and other epithelial tissues; see Barrandon et al., Cell. Vol.50, 1131-1137 (Sep. 25, 1987) incorporated herein by reference. Both EGFand transforming growth factor (TGF), which has the same sequencehomology as EGF and binds to the same cell surface receptor as EGF, havebeen suggested for use in wound healing, Id.; European Patent 190 018(disclosing the use of TGF for the treatment of epithelial and stromalwounds); PCT WO 86/02271 (disclosing the use of human epidermal growthfactor (hEGF) for treating epithelial and stromal wounds); and EuropeanPatent 140 998 (disclosing ophthalmic preparations containing hEGF forthe treatment of keratitis, corneal erosion, corneal infiltration andcorneal ulcers).

Growth factors which can be used according to the present inventioninclude: EGF, fibroblast growth factor (FGF), insulin-like growth factor(IGF), platelet derived growth factor (PDGF), alpha and betatransforming growth factors (TGF_(A) and TGF_(B)) and nerve growthfactor (NGF). In addition, cell enhancing solutions which contain growthfactors can be used, such as SGF-7, available from Scott Laboratories,Inc., and ITS, available from Collaborative Research Incorporated.Growth factors will typically be contained in the compositions of thepresent invention at concentrations between about 0.01 nanograms permilliliter (ng/ml) and 100 micrograms per milliliter (ug/ml). Forexample, EGF can be used at concentrations between about 500 ng/ml and100 ug/ml, preferably between about 10 ug/ml and 50 ug/ml; and FGF canbe used from between about 1.0 ng/ml and 50 ug/ml, preferably at about10 ug/ml. In addition TGF can be used at concentrations of at leastabout 100 ng/ml; see Lawrence et al., Annal. Surg. 203, pp. 142-147(1986).

Basement membrane components can be used to prevent or alleviate scarformation due to improper collagen repair. It has been theorized thatbasement membrane components promote wound healing by contributing tothe reformation of destroyed basement membranes or functioning as abasement membrane, thereby providing a surface across which epithelialcells can migrate and allowing re-epithelialization of the cornea toprogress; see Fujikawa, et al., Fibronectin in Healing Rabbit CornealWounds, Laboratory Investigation, Vol. 45, No. 2, pp. 120-128 (1981)incorporated herein by reference. Basement membranes are thinamporphous, sheetlike structures which separate certain parenchymal celltypes, endothelium and epithelium, from connective tissue stroma. For adiscussion of basement membranes and their role in wound repair; see TheMolecular and Cellular Biology of Wound Repair, Chapter 22, specificallyp. 550 (1986).

In the present invention, basement membrane components are employed toencourage and aid corneal epithelial cells in division, migration andsticking. They influence endothelial cells by providing an attachmentand organizational foundation for the endothelial cells. They also helpwith the organization of collagen in the stroma. Basement membranecomponents which can be used to prevent corneal haze resulting fromimproper collagen repair include: heparin; heparin sulfate; fibronectin;laminin; connective tissue activating peptides such as vinculin;gelatin; glycosaminoglycans; and various types of collagen, especiallytype IV collagen. The present compositions will typically contain one ormore basement membrane components at concentrations between about 0.01ng/ml and 1 milligram per milliliter (mg/ml), preferably about 1 ug/ml.

Regulators of collagen structure can also be used as wound healingmodulators to control or prevent scar formation due to improper collagenrepair. As used herein "regulators of collagen structure" are woundhealing modulators which degrade or inhibit the breakdown of collagen inthe stroma or the collagen released by dead or injured cells; see TheMolecular and Cellular Biology of Wound Repair, at pp. 224-226. Theseregulators can act in two ways, to degrade damaged connective tissue,such as collagen at inflammatory sites, or to act in the reverse mannerinhibiting the degradation of connective tissue. Regulators of collagenstructure which can be used to degrade collagen include, for example:collagenases, elastases, proteases and proline hydroxelase. Regulatorsof collagen structure which will inhibit the degradation of collageninclude all known inhibitors of the aforementioned enzymes includingphenylmethylsulfonyl fluoride (PMSF) and pyrridine-dicarboxylic acidesters used as proline hydroxylase inhibitors, fibrosuppressants andimmunosuppressants as disclosed in U.S. Pat. No. 4,717,727, the contentsof which are hereby incorporated by reference in this specification.Regulators of collagen structure can be used at concentrations ofbetween about 10 ug/ml to about 10 mg/ml.

To prevent or reduce scar formation due to improper epithelial cellcoverage of the cornea after photoablation, various wound healingmodulators can be used. Prior to, or during, photoablation of theanterior surface of the cornea the epithelial cells are removed.Therefore, after surgery it is necessary for re-epithelialization tooccur. Improper epithelial cell coverage leading to scar formation maybe prevented or alleviated through the use of wound healing modulatorsincluding growth factors such as EGF, IGF, PDGF, FGF, TGF_(B), TGF_(A)and NGF and basement membrane components. These wound healing modulatorscan be used at concentrations previously discussed.

In addition, aldose reductase inhibitors (ARIs) can be used as woundhealing modulators according to the present invention. For example,ARIs, such as those disclosed in U.S. Pat. Nos. 4,717,725, 4,600,717,4,436,745, and 4,438,272, 1988, the entire contents of which areincorporated herein by reference, can be used to help prevent cornealhaze from developing due to improper epithelial cell coverage. Thesecompounds inhibit the enzyme aldose reductase. The enzyme's inhibitionappears to be related to the mechanism of wound healing in the diabeticindividual; see Ohasti et al., Aldose Reductase Inhibitor (CT-1121)Eyedrops for Diabetic Corneal Epitheliopathy, American Journal ofOphthalmology, Vol. 105, No. 3 (March, 1988). ARIs can be used atconcentrations between about 0.1 wt. % and 2.0 wt. %.

Concerning corneal haze formation resulting from scar formationattributable to inflammation, the following wound healing modulators canbe used in accordance with the foregoing discussion: steroids; growthfactors such as EGF, FGF, IGF, PDGF, TGF, TGF and NGF, and aldosereductase inhibitors. Additionally, nonsteroidal antiinflammatory agents(NSAIs) can be used as wound healing modulators to prevent or controlcorneal haze resulting from UV photoablation. Nonsteroidalantiinflammatory agents which can be used according to the presentinvention will typically comprise: loxoprofen, as disclosed in BritishPatent No. GB 2,144,993A, published Mar. 12, 1985, incorporated hereinby reference. Compounds disclosed in U.S. Pat. No. 4,559,343, issuedDec. 17, 1985 and incorporated herein by reference can also be used.Those compounds include: flurbiprofen; suprofen; aryl orheteroaryl-carboxylic acids such as mefenamic acid, flufenamic acid,clonixin, flufenisal; aryl or heteroarylalkynoic acids such as4-(t-butyl) benzeneacetic acid, ibufenac, ibuprofen, alkylofenac,fenoprofen, naproxen, indomethacin, tolmetin, ketoprofen and namoxyrate.Additionally, ketorolac, or pyrrolo pyrroles, disclosed in U.S. Pat. No.4,454,151 issued Jun. 12, 1984 and incorporated herein by reference, canbe used. Such NSAIs can be used at concentrations of between about 0.1and 2.0 wt. %. Preferred NSAIs include: suprofen, loxoprofen,flurbiprofen, indomethacin and ketorolac. These compounds are typicallypresent in the compositions at the following concentrations: suprofen atabout 1.0 wt. %, loxoprofen at about 1.0 wt. %, flurbiprofen at about0.25 wt. %, indomethacin from about 0.1 to 1.0 wt. % and ketorolac atabout 0.5 to 1.0 wt. %.

Anti-oxidants can also be used as wound healing modulators to control orprevent scar formation resulting from inflammation followingphotoablation of the cornea. When tissue, such as the cornea, issubjected to trauma, for example laser radiation, reactive species inexcess of those normally present as a result of enzymatic andnonenzymatic reactions are produced. These reactive species, includingfree radicals, can cause tissue damage; see The Molecular and CellularBiology of Wound Repair, specifically Chapters 1, 6 and 7; and Fisher,Intracellular Production of Oxygen Derived Free Radicals, OxygenRadicals and Tissue Injury, Proceedings of a Book Lodge Symposium (April1987), which is incorporated herein by reference. Anti-oxidants preventscar formation by scavenging free radicals. Suitable anti-oxidantsinclude, for example: ascorbic acid; glutathione; see Meister, SelectiveModification of Glutathione Metabolism, Science, Vol. 220 (April, 1988);alpha tocopherol; and selenous acid or sodium selenate. Suchanti-oxidants can be used at concentrations between about 0.001 ng/mland 1 mg/ml, preferably about 100 ng/ml.

Immunomodulators can also be used to control inflammation which maycontribute to the appearance of corneal haze. Immunomodulators which maybe used include: cyclosporin A and cyclosporin G, leflunomide,N-(4-trifluoromethylphenyl)-N-(2-cyano-1-hydroxy-1-propen-1-yl)carboxamideand interferon (γ,β and α). Immunomodulators can be used atconcentrations between about 2 and 10 wt. %.

Antiallergics are wound healing modulators which can also be used toprevent corneal haze resulting from scar formation due to inflammation.This class of compounds includes for example: cyproheptadine,dipheniramine, azelastine, cimetidine, neodocromil, cromolyn,lodoxamide, pheniramine and6-methyl-N-(1H-tetrazol-5yl)-z-pyridinecarboxamide. Such antiallergiccompounds can be used at concentrations of about 0.1 to 4.0 wt. %.

As indicated above, a second possible explanation for the development ofcorneal haze resulting from photoablation of the cornea is that thefibroblasts of the stroma may be improperly activated in response to thelaser irradiation. As a result the fibroblasts aberrantly metabolizecellular components, such as extracellular matrix proteins in anunhealthy, unorganized fashion. These components appear as specks in thestroma observable as a granular corneal haze.

Wound healing modulators which can be used to prevent or alleviatecorneal haze resulting from improperly activated fibroblasts include:growth factors, such as EGF, FGF, TGF_(A), TGF_(B), NGF, PDGF, insulinlike growth factor (IGF) and insulin; and tumor necrosis factor (TNF).Such growth factors can be used in accordance with the foregoingdiscussion of this class of wound healing modulators. In addition, theimmunomodulators, antiallergics and basement membrane components, aspreviously set forth, can be used in this situation.

A third possible explanation for the appearance of corneal hazefollowing photoablation of the cornea involves radiation damage ofcollagen fibrils resulting in improper alignment within the stroma. Theclear character of the cornea is in part dependent on the properconfiguration and spacing of the collagen fibrils within the stroma.Therefore, improper alignment may appear as specks or haze in thestroma.

Wound healing modulators which can be used to prevent or alleviate theformation of corneal haze due to damage to collagen fibrils include: thegrowth factors TNF, EGF, FGF, IGF and insulin; steroids;immunomodulators, basement membrane components and antioxidants, all ofwhich may be used as previously discussed.

A fourth possible explanation for the formation of corneal haze is thatthe laser may kill or damage fibroblasts in the stroma. A deadfibroblast will cease functioning relative to proper formation of thecollagen matrix and can also act as a refractive object until absorbed.If the fibroblast is damaged, but not killed by the laser, it couldcontinue functioning but possibly in a faulty manner due to DNA damage.For example, fibroblasts make a procollagen molecule that could beimproperly enzymatically clipped resulting in secretion of defectivecollagen.

Wound healing modulators which can be used to combat corneal hazeresulting from dead or damaged fibroblasts include the growth factorsEGF, FGF, PDGF, TGF_(A), TGF_(B) and NGF, all of which may be used aspreviously discussed. In addition, fatty acid derivatives, which areproducts of the arachidonic acid cascade such as cyclo-oxygenaseproducts (prostaglandins and thromboxanes which down regulate) andleukotrienes (LTB₄ and LTC₄ which up regulate) can contribute to thetreatment of corneal haze by stimulating polymorphonuclear leukocytes(PMN), macrophages and fibroblasts, thereby increasing clearance of thecorneal haze. For a discussion regarding the regulation ofmacrophage-derived fibroblast growth factor, which is involved in woundhealing and scar formation, by arachidonate metabolites, see Journal ofLeukocyte Biology 42:106-113(1987), the contents of which areincorporated herein by reference. Immunomodulators can also be used inthis situation to control the activity of lymphocytes, which cancontribute to the prevention and treatment of corneal haze in accordancewith the foregoing discussion of this class of compounds.

A fifth possible cause of the corneal haze is the corneal edema whichmay occur following photoablation. Wound healing modulators which can beused to combat the formation of and treat corneal haze attributable toedema include: growth factors such as EGF, FGF, TGF_(A) TGF_(B) and NGF;steroids; nonsteroidal antiinflammatories; antiallergics; anti-oxidantsand aldose reductase inhibitors. Additionally antimicrobial compounds,discussed below, can be particularly useful in treating corneal hazeattributable to edema.

Photoablation leaves the cornea denuded of its protective epitheliallayer leaving it prone to infection. Antimicrobials can be usedaccording to the present invention pre-operatively and post-operativelythereby safeguarding against corneal infection which inhibits healing,possibly leading to corneal edema and the formation of corneal haze.Antimicrobials which can be used according to the present inventioninclude: chloramphenicol, erythromycin, gentamycin, polymyxin,sulfacetamide, tetracycline, tobramycin, sulfisoxazole, diolamine,ciprofloxacin, natamycin, neomycin, ofloxacin, norfloxacin,trifluorothymidine, acyclovir, gancyclovir, vancomycin and otherantibacterial, antiviral and antifungal agents. The compositionscomprise one or more antimicrobials or combinations of antimicrobialsand other wound healing modulators. Such antimicrobials are used atconcentrations between about 0.05 and 3.0 wt. %. preferably less thanabout 1.0 wt. %.

As set forth above, it is believed corneal haze resulting from laserirradiation is related to one or more of the following: wound repair;improperly activated fibroblasts; damaged collagen fibrils; damaged ordead fibroblasts in the stroma; and corneal edema. Corneal haze may beprevented with varying degrees of success with steroids, growth factors,basement membrane components, regulators of collagen structure, aldosereductase inhibitors, NSAIs, antioxidants, immunomodulators andantiallergics (which are particularly effective against corneal hazeresulting from wound repair); growth factors, immunomodulators,antiallergics and basement membrane components (which are particularlyeffective when fibroblasts of the stroma have been improperlyactivated); growth factors, steroids, immunomodulators, basementmembrane components and antioxidants (which are particularly effectivein alleviating the formation of corneal haze due to damaged collagenfibrils); growth factors and fatty acid derivatives of the arachidonicacid cascade (which are particularly effective when damaged or deadfibroblasts are present); and growth factors, steroids, NSAIs,antiallergics, anti-oxidants, aldose reductase inhibitors andantimicrobials (which are particularly effective in treating cornealhaze attributable to edema).

The wound healing modulators of the present invention can be appliedalone or in combination with other wound healing modulators. Inaddition, individual wound healing modulators or combinations thereofcan be applied uniquely or sequentially. While the effective dose andtreatment regime are left to the discretion of the clinician, thefollowing procedures are recommended.

The wound healing modulators which can be used to prevent or alleviatecorneal haze are formulated in compositions for topical application tothe eye. As will be appreciated by those skilled in the art, thecompositions can be formulated in various pharmaceutically acceptableforms for topical ophthalmic delivery including: solutions, suspensions,emulsions, gels and solid inserts, depending on the nature andcharacteristics of the wound healing modulators. Preferred formulationsare aqueous solutions. In addition, the wound healing modulators of thepresent invention can be applied via the use of a collagen shield,contact lens or other solid matrix placed on the ocular surface. Suchshields, lenses or matrices can provide for slow release of themodulators as well as serving as a protective environmental barrier.

In addition to the principal active ingredients, the wound healingmodulator compositions of the present invention may further comprisevarious formulatory ingredients, such as antimicrobial preservatives andtonicity agents. For example, antimicrobial preservatives include:benzalkonium chloride, thimerosal, chlorobutanol, methylparaben,propylparaben, phenylethyl alcohol, EDTA, sorbic acid, POLYQUAD andother agents equally well known to those skilled in the art. Suchpreservatives, if employed, will typically be used in an amount fromabout 0.0001 wt. % to 1.0 wt. %. Suitable agents which may be used toadjust tonicity or osmolality of the compositions include: sodiumchloride, potassium chloride, mannitol, dextrose glycerine and propyleneglycol. If used, such agents will be employed in an amount of about 0.1wt. % to 10.0 wt. %. However, preferable compositions of the presentinvention will not include preservatives or tonicity agents which areknown to adversely affect or irritate the eye, particularly the cornea.

As will be understood by those skilled in the art, the administration,sequence of administration when more than one wound healing modulator isused, and the concentrations of the wound healing modulators useddepends on numerous factors. These factors can include: the specificwound healing modulator or modulators being used, the nature of thesurgical procedure, and various clinical factors, including the extentand type of haze being treated, the medical history of the patient,symptoms apparent prior to, during, or after surgery, such asinflammation or edema, etc. Selection of specific wound healingmodulators or combinations thereof, their concentrations and sequence ofdelivery to the eye will be made by the skilled clinician guided by theforegoing description.

Regardless of the reason or combination of reasons for development ofcorneal haze, there are compounds, or compositions, collectivelyreferred to herein as "adjuncts" which can be used alone, or in additionto the wound healing modulators discussed above, that contribute to theoverall health and comfort of the eye, thus contributing to theprevention of corneal haze and its treatment.

For example, during and following photoablation of the cornea, elevationof intraocular pressure may occur. Control of intraocular pressurecontributes to the health of the cornea thereby allowing the cornea toheal without resulting corneal haze. Adjuncts for controllingintraocular pressure which can be used in combination with wound healingmodulators include antihypertensive agents. Antihypertensive agentswhich can be used include, for example, timolol, betaxolol, levobunalol,glycerin, isosorbide, manitol, urea, paraminoclonidines, epinephrine andcarbonic anhydrase inhibitors. The compounds can be topically applied tothe eye following photoablation at concentrations between about 0.1 and2.0 wt. % preferably about 0.5 wt. %. In addition, miotics can be usedto control intraocular pressure. For example miotics such as carbachol,pilocarpine, physostigmine, echothiophate and isofluorphate can be used.

Humectants may be used prior to, during and after photoablation of thecornea. These adjuncts promote healing of the cornea by providinglubrication and preserving the natural tear physiology. Humectants caninclude preparations which typically comprise hydroxyethylcellulose,hydroxypropylcellulose, hydroxypropylmethylcellulose, methylcellulose,polyvinyl alcohol, cellulose esters, povidone or other suitablepolymeric systems.

Epithelial cell health promoters as used herein, are compounds known tocontribute to the health of the epithelial cells of the cornea. Thepresence of these compounds prior to, during, and/or after photoablationof the cornea can contribute to the prevention of corneal haze byencouraging the rapid resumption of epithelial integrity and preventionof stromal edema. Epithelial cell health promoters which can be used asadjuncts to the wound healing modulators of the present invention caninclude: ascorbic acid; retinoids, such as retinoic acid, retinol,retinal and retinoyl B-glucuronide; aloe vera; collagenase inhibitors;prostaglandins, such as prostaglandin E and elastase inhibitors.

The present invention also encompasses methods of treatment of an eyeexposed to laser radiation during ophthalmic procedures. Methods oftreatment, during ophthalmic surgery, with compositions containing woundhealing modulators, as disclosed above, include application of thecompositions before laser exposure, during the procedures, for examplewhen the eye is moistened and a wet keratoscope reading is taken duringcorneal sculpting using a laser and/or immediately after irradiation. Inaddition, and as previously discussed, the compositions of the presentinvention can be applied uniquely or when the use of more than one woundhealing modulator is indicated, the medicaments can be administeredsequentially.

The following formulation is an example of a wound healing modulatorcomposition that can be used for the prevention and treatment of cornealhaze resulting from laser irradiation. It is not limiting but consideredrepresentative of useful compositions of the present invention.

EXAMPLE

The following composition can be formulated by mixing the specificcomponents at the indicated concentrations. The compositions should beeither prepared under sterile conditions or sterilized after theirpreparation and prior to their use.

EXAMPLE 1 (Suspension)

    ______________________________________                                        Component           Concentration                                             ______________________________________                                        Dexamethasone       0.1 wt. %                                                 Neomycin Sulfate    Equivalent to Neomycin                                                        3.5 mg/ml                                                 Polymixin Sulfate   10,000 units/ml                                           Benzalkonium Chloride                                                                             0.0004 wt. %                                              Hydroxypropyl Methylcellulose                                                                     0.5 wt. %                                                 Purified Water      q.s.                                                      ______________________________________                                    

We claim:
 1. A method for treating corneal haze as an artifact ofincident laser irradiation and resulting photoablation of corneal tissuecomprising:applying to the affected eye, a therapeutically effectiveamount of a steroid.
 2. The method of claim 1 wherein the steroid isdexamethasone.
 3. The method of claim 1 wherein the steroid is presentat a concentration of about 0.1 to 4.0 wt. %.
 4. The method of claim 1wherein the steroid is prednisolone.
 5. The method of claim 1 whereinthe steroid is fluoromethlone.